This invention relates to a vacuum activated apparatus for picking up, releasably grasping and transporting a thin solid object such as a semiconductor wafer. Further, this invention relates to a vacuum activated apparatus, for releasably grasping a single crystal silicon semiconductor wafer, having a guiding element for controlling and directing the wafer to the grasping surface of the apparatus.
It is well known that in industrial processes the grasping, transport and manipulation of small, thin, flat objects can present numerous problems. This is especially true in the electronics industry and even more especially true in the semiconductor industry. Single crystal silicon semiconductor wafers, used to make integrated circuit chips for watches, calculators, instruments and other devices, are thin and brittle. They are easily broken and their surfaces are especially susceptible to scratches and contamination. Such scratches and contamination destroy the usefulness of the wafer for integrated circuit manufacture. Thus, the wafer must be handled with care during its production and subsequent processing into integrated circuit chips. Further, breakage, scratching and contamination of the wafer reduce the yield of the wafer manufacturer. This reduced yield, of course, increases the cost of the wafer. It is thus important to have a handling apparatus that does not break, scratch or contaminate the wafer and yet permits the easy, rapid pick up and handling of the wafer.
A number of steps are employed in the manufacture of a single crystal silicon semiconductor wafer starting with the single crystal silicon rod from which the wafer is cut. The wafer is, during its manufacture, lapped or ground to a uniform thickness and flat surfaces. One flat surface is then polished, and the wafer is cleaned, etched and cleaned again. In many instances, an epitaxial layer of single crystal silicon is then desposited on the polished surface of the wafter at an elevated temperature. This deposition usually occurs from the vapor phase on to the wafer surface generally at a temperature of about 1000.degree. C. to 1300.degree. C. In many of the modern reactors for the elevated temperature vapor deposition of the single crystal silicon epitaxial layer onto the surface of the silicon wafer, the wafer is held in a substantially vertical position on the surface of a rotatable graphite drum or barrel known as a susceptor. This configuration permits a larger number of wafers to be processed in the reactor at one time than is possible with a horizontal placement of the wafers in a reactor of the same size. The surface of the drum is inclined slightly and has depressions into which the wafers fit. This inclination is just sufficient to prevent the wafers from falling out of the depressions in the surface of the drum or barrel susceptor. To remove the wafer from the surface of the barrel type susceptor the wafer must be tipped forward from the base of the depression in which it sits and at the same time be grasped at its rear surface to prevent the wafer from falling from the susceptor and breaking. The removal of the wafer from the susceptor is usually done while the susceptor and wafer are still very warm or hot, e.g. 200.degree. to 300.degree. C. This improves reactor utilization since there is no waiting for the reactor to cool to room temperature before removing the wafers and reloading the reactor. Metal tweezers have been used to remove the hot wafer from the susceptor because of their resistance to heat, however, they tend to (1) scratch the epitaxial layer and the opposite face of the silicon semiconductor wafer and (2) contaminate the epitaxial layer and the opposite face of the wafer. To overcome the problems with metal tweezers, plastic tipped metal tweezers and even plastic tweezers have been tried and found to be undesirable not only because they also may contaminate the epitaxial layer and the opposite side of the wafer but they also are found to have insufficient resistance to the heat present in the wafer. These mechanical metal and plastic tweezers also make it difficult to tip the wafer away from the barrel type susceptor and grasp it before the wafer falls from the susceptor. Quartz tip vacuum pencils as are used in the art to pick up a wafer from a horizontal surface or remove a wafer from a storage tray or rack have also been found to be not entirely suitable for removing wafers from a barrel type susceptor because the insertion of the flat spatula like or wedge shaped quartz tip between the wafer and the surface of the barrel type susceptor moves the wafer away from the susceptor far enough to allow the wafer to fall from the susceptor before the wafer can be grasped by the tip by applying a vacuum. Thus, prior art apparatus for grasping and handling semiconductor wafers have not been found to be entirely suitable for placing wafers on and removing wafers from a barrel type susceptor of an epitaxial ractor.
It is an object of this invention to provide an apparatus to releasably grasp a semiconductor wafer while avoiding scratching, contaminating or otherwise damaging the wafer.
Another object of this invention is to provide an apparatus to releasably grasp a semiconductor wafer or other thin solid article to safely lift the wafer or article from a surface.
A still further object of this invention is to provide an apparatus to remove a semiconductor wafer from a vertical susceptor surface.
An even further object of this invention is to provide an apparatus wherein a means is provided to guide and direct a semiconductor wafer or other thin solid article toward and on to a grasping surface to releasably grasp the wafer or the article under vacuum for lifting, transporting or depositing the wafer or article, without contacting the front surface.
These and other objects of this invention will become apparent from the following more detailed description.